Power savings mode for ocean bottom seismic data acquisition systems

ABSTRACT

Embodiments of the invention provide methods, systems, and apparatus for conserving power while conducting an ocean bottom seismic survey. Sensor nodes placed on an ocean floor may be configured to operate in at least an idle mode and an active mode. Each node may adjust its mode of operation from idle mode to active mode.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority to and the benefit of U.S. provisionalapplication No. 61/775,915 entitled “Power Savings Mode for Ocean BottomSeismic Data Acquisition Systems,” which was filed on Mar. 11, 2013, andwhich is hereby incorporated by reference in its entirety for allpurposes.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention generally relates to seismic data acquisition, andmore specifically to ocean bottom seismic data acquisition systems.

2. Description of the Related Art

In conventional marine seismic surveying, a vessel tows a seismicsource, such as an airgun array, that periodically emits acoustic energyinto the water to penetrate the seabed. Sensors, such as hydrophones,geophones, and accelerometers may be housed in sensor units at sensornodes periodically spaced along the length of an ocean bottom cable(OBC) resting on the seabed. Alternatively, a plurality of autonomoussensor nodes, each comprising one or more seismic sensors may bedeployed on the seabed. The sensors of the sensor node are configured tosense acoustic energy reflected off boundaries between layers ingeologic formations. Hydrophones detect acoustic pressure variations;geophones and accelerometers, which are both motion sensors, senseparticle motion caused by the reflected seismic energy. Signals fromthese kinds of sensors are used to map the geologic formations.

The power required to operate the sensor nodes may be provided viabatteries and/or power generators. For example, in OBC systems, thecable may be connected to a surface buoy or a seismic vessel comprisinga generator, e.g., a diesel generator. The generator may provide powerfor operating the sensors either directly or indirectly (e.g., viachargeable batteries). In autonomous sensor node based system,rechargeable batteries may be included in each node to power the node.

SUMMARY OF THE INVENTION

The present invention generally relates to seismic data acquisition, andmore specifically to ocean bottom seismic data acquisition systems.

One embodiment of the invention provides a method for marine seismicdata collection. The method generally comprises operating a sensor nodein an idle mode, wherein the idle mode is configured to conserve powerconsumption by the sensor node, and determining whether seismic data isexpected at the sensor node. The method further comprises operating thesensor node in an active mode in response to determining that seismicdata is expected, and collecting seismic data while in the active mode.

Another embodiment of the invention provides a method for conducting aseismic survey. The method generally comprises deploying a plurality ofsensor nodes on a seabed, wherein the sensor nodes are initiated tooperate in an idle mode, initiating operation of a seismic source boat,wherein the seismic source boat is configured to generate a signal tothe sensor nodes, and selectively adjusting a mode of operation of oneor more sensor nodes from the idle mode to an active mode based on aproximity of the one or more sensor nodes to the source boat, whereinthe proximity is determined based on the signal.

Yet another embodiment of the invention provides an ocean bottom seismicsensor node generally comprising a processor, at least one acousticsensor, at least one particle motion sensor, and a memory. The memorycomprises a mode selection program which, when executed by the processoris configured to perform operations comprising operating the sensor nodein an idle mode, wherein the idle mode is configured to reduce powerconsumption by the sensor node, determining whether seismic data isexpected at the sensor node, in response to determining that seismicdata is expected, operate the sensor node in an active mode, andcollecting seismic data while in the active mode.

BRIEF DESCRIPTION OF THE DRAWINGS

So that the manner in which the above recited features, advantages andobjects of the present invention are attained and can be understood indetail, a more particular description of the invention, brieflysummarized above, may be had by reference to the embodiments thereofwhich are illustrated in the appended drawings.

It is to be noted, however, that the appended drawings illustrate onlytypical embodiments of this invention and are therefore not to beconsidered limiting of its scope, for the invention may admit to otherequally effective embodiments.

FIG. 1 is an example of a seismic survey according to an embodiment ofthe invention.

FIG. 2 is an example of a seismic survey according to another embodimentof the invention.

FIG. 3 is yet another example of a seismic survey according to anembodiment of the invention.

FIG. 4 illustrates a sensor node according to an embodiment of theinvention.

FIG. 5 illustrates a hub device according to an embodiment of theinvention.

FIG. 6 is a flow diagram of exemplary operations performed by a sensornode, according to an embodiment of the invention.

FIGS. 7A-7B illustrate exemplary output from an acoustic sensor,according to an embodiment of the invention.

FIG. 8 illustrates a plan view of a seismic survey according to anembodiment of the invention.

FIG. 9 is a flow diagram of exemplary operations performed whileconducting a seismic survey according to an embodiment of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Embodiments of the invention provide methods, systems, and apparatus forconserving power while conducting an ocean bottom seismic survey. Sensornodes placed on an ocean floor may be configured to operate in at leastan idle mode and an active mode. When a seismic source boat approachesthe sensor node, the node may adjust its mode of operation from an idlemode to an active mode. After the seismic source boat is no longer nearthe sensor node, the idle mode may be entered again to conserve power.

In the following, reference is made to embodiments of the invention.However, it should be understood that the invention is not limited tospecific described embodiments. Instead, any combination of thefollowing features and elements, whether related to differentembodiments or not, is contemplated to implement and practice theinvention. Furthermore, in various embodiments the invention providesnumerous advantages over the prior art. However, although embodiments ofthe invention may achieve advantages over other possible solutionsand/or over the prior art, whether or not a particular advantage isachieved by a given embodiment is not limiting of the invention. Thus,the following aspects, features, embodiments and advantages are merelyillustrative and are not considered elements or limitations of theappended claims except where explicitly recited in a claim(s). Likewise,reference to “the invention” shall not be construed as a generalizationof any inventive subject matter disclosed herein and shall not beconsidered to be an element or limitation of the appended claims exceptwhere explicitly recited in a claim(s).

One embodiment of the invention is implemented as a program product foruse with a computerized system. The program(s) of the program productdefines functions of the embodiments (including the methods describedherein) and can be contained on a variety of computer-readable media.Illustrative computer-readable media include, but are not limited to:(i) information permanently stored on non-writable storage media (e.g.,read-only memory devices within a computer such as CD-ROM disks readableby a CD-ROM drive); (ii) alterable information stored on writablestorage media (e.g., floppy disks within a diskette drive or hard-diskdrive); and (iii) information conveyed to a computer by a communicationsmedium, such as through a wireless network. The latter embodimentspecifically includes information downloaded from the Internet and othernetworks. Such computer-readable media, when carrying computer-readableinstructions that direct the functions of the present invention,represent embodiments of the present invention.

In general, the routines executed to implement the embodiments of theinvention, may be part of an operating system or a specific application,component, program, module, object, or sequence of instructions. Thecomputer program of the present invention typically is comprised of amultitude of instructions that will be translated by the native computerinto a machine-readable format and hence executable instructions. Also,programs are comprised of variables and data structures that eitherreside locally to the program or are found in memory or on storagedevices. In addition, various programs described hereinafter may beidentified based upon the application for which they are implemented ina specific embodiment of the invention. However, it should beappreciated that any particular program nomenclature that follows isused merely for convenience, and thus the invention should not belimited to use solely in any specific application identified and/orimplied by such nomenclature.

FIG. 1 illustrates an exemplary seismic survey according to anembodiment of the invention. A plurality of autonomous sensor nodes 110may be deployed on the seabed 111. Any reasonable means may be used todeploy the autonomous sensor nodes 110. For example, in one embodiment,the sensor nodes 110 may be deployed on the sea floor or bed using aremotely operated vehicle (ROV, not shown). Alternatively, each of theautonomous sensor nodes 110 may be attached to a rope, and deployed tothe seabed directly from a boat. In yet another embodiment, eachautonomous sensor node may be equipped and programed to navigate throughthe water column to and from predetermined locations on the sea floor.

While reference is made to a sea floor and seabed herein, embodiments ofthe invention are not limited to use in a sea environment. Rather,embodiments of the invention may be used in any marine environmentincluding oceans, lakes, rivers, etc. Accordingly, the use of the termsea, seabed, sea floor, and the like, hereinafter should be broadlyunderstood to include all bodies of water.

Referring back to FIG. 1, a source boat 120 may be configured to tow aseismic source 121 while conducting a seismic survey. In one embodiment,the seismic source 121 may be an air gun configured to release a blastof compressed air into the water column towards the seabed 111. As shownin FIG. 1, the blast of compressed air generates seismic waves 122 whichmay travel down towards the seabed 111, and penetrate and/or reflectfrom sub-seabed surfaces. The reflections from the sub-surfaces may berecorded by the nodes 110 as seismic data, which may be thereafterprocessed to develop an image of the sub-surface layers. These imagesmay be analyzed by geologists to identify areas likely to includehydrocarbons or other substances of interest.

FIG. 2 illustrates another example of a seismic survey according to anembodiment of the invention. As illustrated in FIG. 2, a plurality ofsensor nodes 210 may be placed in each of one or more ocean bottomcables (OBCs) 230. In one embodiment, the OBCs may be coupled to arespective surface buoy 231. The surface buoys may include seismic datastorage systems configured store seismic data collected by the sensornodes 210. The surface buoys 231 may also include a power system 232.The power system 232, in one embodiment, may include one or more of agenerator, e.g., a diesel generator, one or more rechargeable batteries,fuel cell, and the like.

A cable 233 may be included in each of the OBCs 230 for transferringpower, data, instructions, and the like from the surface buoy 231 to thesensor nodes 210 in the OBC. In one embodiment, the cable 233 mayinclude a plurality of transmission lines. For example, a firstplurality of transmission lines may be configured to transfer databetween the sensor nodes and the buoy 231, a second plurality of datalines may be configured to transfer instructions between the sensornodes and the buoy 231, and a third one or more transmission lines maytransfer power from the buoy 231 to the sensor nodes. In alternativeembodiments, the same set of transmission line or lines may be used totransfer one or more of seismic data, instructions, and/or power.Moreover, while a single cable 233 is referred to herein, in alternativeembodiments, a plurality of cable segments may be included to transferthe seismic data, instructions, and power between the sensor nodes 210and respective buoy 231.

In one embodiment of the invention, the sensor nodes 210 may be coupledto each other serially. Therefore, each node may be configured toreceive and transfer instructions, data, power, etc. from a first nodeto a second node. In an alternative embodiment, the sensor nodes 210 maybe connected in parallel via the cable 233. In other words, each sensornode 210 may be directly coupled to the surface buoy 231 via the cable233. In other embodiments, the sensor nodes may be connected in anycombination of serial and parallel connections with respect to eachother, and direct and indirect coupling with the surface buoy.

In FIG. 2, while each cable 230 is shown to be coupled with its ownrespective surface buoy 231 in FIG. 2, in alternative embodiments,multiple cables 230 may be coupled to a single buoy 231. In otherembodiments of the invention, the surface buoys 231 may be omitted, andthe cables 230 may be coupled to a recording boat, which may includerecording and power generation equipment to support the sensor nodes210.

FIG. 2 further illustrates a source boat 220, seismic source 221, andseismic waves 222 which correspond to the source boat 120, seismicsource 121, and seismic waves 122, respectively. While a single source121 and 221 is shown in each of FIGS. 1 and 2, in alternativeembodiments, a plurality of sources may be used while conducting aseismic survey. When a plurality of sources is used, the sources may bearranged in a source array that is towed behind the source boat.

While the sensor nodes 210 are depicted as being enclosed within anocean bottom cable skin, in alternative embodiments, the sensor nodes210 may not be enclosed as shown. In such alternative embodiments, thesensor nodes may be independent distinct devices exposed to the water,and may be strung together via a single cable or cable segments.Accordingly, reference to the term “ocean bottom cable” herein refers toany reasonable arrangement of sensor nodes wherein a plurality of sensornodes are physically coupled to each other, whether or not they areenclosed in a cable skin.

FIG. 3 illustrates yet another embodiment of the invention. Similar toFIG. 2, the seismic survey shown in FIG. 3 may also include a sourceboat 320 towing one or more seismic sources 321 and a plurality of oceanbottom cables 330, each comprising a plurality of nodes 310. In contrastto FIG. 2, however, the ocean bottom cables 330 may be coupled to asub-sea hub 331 instead of a surface buoy. In one embodiment, as shownin FIG. 3, the sub-sea hub 331 may be placed on the sea floor.Alternatively, in other embodiments, the sub-sea hub may be configuredto float at a predefined distance above the sea floor or a predefineddistance below the water surface. The use of sub-sea hubs 331 may beparticularly advantageous in environments such as the arctic, where thesea surface may be frozen and/or may include moving masses of ice whichmay crash into and destroy surface buoys.

As in the case of the surface buoy 231 of FIG. 2, the sub-sea hub 331also includes a power system 332 (which is similar to the power system232), and power cable 333 (which is similar to the power cable 233) forproviding power to the nodes 310.

FIG. 4 illustrates a mode detailed view of a sensor node 400 accordingto an embodiment of the invention. The sensor node may be an example ofany one of the sensor nodes 110, 210, and 310 illustrated respectivelyin FIGS. 1, 2, and 3, but is not limited to those embodiments. Asillustrated in FIG. 4, the sensor node 400 may include a CentralProcessing Unit (CPU) 411, a memory 412, one or more seismic sensors420, storage 416, one or more clocks 430, and a network interface device419, and an energy storage system 440. While a single CPU 411 is shownin FIG. 4, in alternative embodiments, a plurality of CPUs may beimplemented within the node 400.

The network interface device 419 may be any entry/exit device configuredto allow network communications between the sensor node 400 and anotherdevice, e.g., another sensor node, surface buoy, or sea-bed hub, or thelike, via a network, e.g., a wireless network, the cables 233 and 333shown in FIGS. 2 and 3, or the like. In one embodiment, the networkinterface device 419 may be a network adapter or other network interfacecard (NIC).

Storage 416 is preferably a Direct Access Storage Device (DASD).Although it is shown as a single unit, it could be a combination offixed and/or removable storage devices, such as fixed disc drives,floppy disc drives, tape drives, removable memory cards, or opticalstorage. The memory 412 and storage 416 could be part of one virtualaddress space spanning multiple primary and secondary storage devices.

The seismic sensors 420 may be configured to record seismic signals. Inone embodiment, the seismic sensors may include one or more particlemotion sensors 414 and one or more acoustic sensors 415, as illustratedin FIG. 4. The acoustic sensors 415 may be configured to measure apressure wavefield. In one embodiment, the acoustic sensor may be ahydrophone. The particle motion sensors may be configured to detect atleast one component of particle motion associated with an acousticsignal. Examples of particle motion sensors include geophones, particledisplacement sensors, particle velocity sensors, accelerometers, orcombinations thereof.

The clocks 430 may be utilized to determine the arrival times of variousacoustic signals. As illustrated in FIG. 4, the clocks 430 may include ahigh precision clock 417 and a low precision clock 418, according to oneembodiment. The high precision clock 417 may be used to operate thesensor node in an acquisition or active mode, and the low precisionclock 418 may be used to operate the device in an idle or sleep or powersavings mode, as will be described in greater detail below.

The energy storage system 440 may be configured to power operation ofthe sensor node 400. In one embodiment, the energy storage system 440may be a rechargeable battery system including one or more batteriesmade from, e.g., nickel-cadmium (NiCd), nickel-zinc (NiZn), nickel metalhydride (NiMH), and/or lithium-ion (Li-ion) based cells. In analternative embodiment, the energy storage system may include a fuelcell. Exemplary fuels that may be used as fuel in the fuel cell includehydrogen, hydrocarbons such as natural gas or diesel, and alcohols suchas methanol. In some embodiments, a combination of different types ofenergy storage systems may be integrated within the energy storagesystem 440 to power the sensor node 400.

In one embodiment of the invention, the energy storage system may bereplenished from an external source. For example, in a battery basedenergy storage included in an OBC embodiment, a cable (e.g., the cables233 and 333) may be used to recharge the energy storage systemperiodically.

The memory 412 is preferably a random access memory sufficiently largeto hold the necessary programming and data structures of the invention.While memory 412 is shown as a single entity, it should be understoodthat memory 412 may in fact comprise a plurality of modules, and thatmemory 412 may exist at multiple levels, from high speed registers andcaches to lower speed but larger DRAM chips.

Illustratively, the memory 412 contains an operating system 413.Illustrative operating systems, which may be used to advantage, includeLinux (Linux is a trademark of Linus Torvalds in the US, othercountries, or both). More generally, any operating system supporting thefunctions disclosed herein may be used.

Memory 412 is also shown containing a mode selection program 423 which,when executed by CPU 411, provides support selecting an operating modefor the sensor node 400. For example, the mode selection program 423 maybe configured to determine a predefined mode selected from a set ofpredefined operating modes to operate the sensor node. Exemplaryoperating modes may include an active or operating mode and a sleep oridle or power savings mode, as will be described in greater detailbelow. While the mode selection program 423 is shown as being separatefrom the operating system 413 in FIG. 4, in alternative embodiments, themode selection program 423 may be a part of the operating system oranother program.

FIG. 5 is an example of an exemplary hub device 500, according to anembodiment of the invention. The hub device 500 may be an example of thesurface buoy 231 of FIG. 2 and the sea-bed hub 331 of FIG. 3. The hub500 may be physically arranged in a manner similar to the sensor node400. Accordingly, the hub 500 is shown generally comprising one or moreCPUs 511, a memory 522, and a storage device 533.

Memory 522 may be a random access memory sufficiently large to hold thenecessary programming and data structures that are located on the hub500. As shown in FIG. 5, the memory 522 may include an operating system523 and a node selection program 524. In one embodiment, the nodeselection program 524 may be configured to instruct one or more sensornodes associated with the hub device to enter into one of a predefinedset of operating modes, as will be described in greater detail below.

The hub 500 may also include a power system 540. As illustrated in FIG.5, the power system 540 may include a power generator 541 and an energystorage system 542. The energy storage system 542 may be similar to theenergy storage system 440 of FIG. 4, and may include, e.g., one or morebatteries. The power generator can be any type of power generator, forexample, a diesel generator, fuel cell, solar panels, and the like. Ingeneral, the power generated by the generator 541 and/or the powerstored in the energy storage system 542 may be supplied to one or moresensor nodes. For example, the sensor nodes may be configured to operatebased on such supplied power, in one embodiment. Alternatively, suchsupplied power may be used to recharge the energy storage system 440within the sensor nodes.

In one embodiment, the hub 500 may include one or more acoustic sensors550. The acoustic sensors 550 may facilitate communications between thehub 500 and a source boat, as will be described in greater detail below.

Referring back to the seismic surveys illustrated in FIGS. 1-3, thetotal area of the sea floor that may be covered by survey operations mayexpand for several hundreds, if not thousands, of square miles.Deploying autonomous sensor nodes and/or ocean bottom cables on the seafloor may be a task that takes several days, if not weeks. The actualsurvey and seismic data collection itself may continue for severalmonths. Furthermore, events such as bad weather, malfunctions in thesensor node deployment systems, and the like can introduce heavy delayswhich may last several days in some instances.

Given the large amount of time that the sensor nodes may have to remainon the ocean bottom, it is critical that there is sufficient power tooperate the sensor nodes while they are on the sea floor. However, thetotal available power in the energy storage and generation systems ofthe sensor nodes and hubs may only be sufficient to operate the sensornodes for a few short weeks. Embodiments of the invention providemethods, systems, and apparatus for efficiently using the availablepower so that the life of the sensor nodes is extended while they are onthe ocean floor.

In one embodiment of the invention, the sensor nodes may be configuredto operate in one of a plurality of predefined operating modes. Forexample, one mode of operation may include an active mode. In the activemode, all or most of the components of the sensor node may be fullypowered. The active mode may be entered at a time when seismic datacollection is expected.

The sensor nodes may also be configured to operate in a sleep/idle/powersavings mode (hereinafter referred to simply as idle mode). In the idlemode, the sensor node may be configured to turn off power to one or moredevices and/or operate certain devices in a low power mode. For example,referring back to FIG. 4, the mode selection program 423 may beconfigured to cause the CPU 411 to enter a power savings mode ofoperation while in the idle mode. In one embodiment, operating the CPU411 in the low power mode may involve dynamic voltage scaling and/ordynamic frequency scaling, which may alter the CPU core voltage and/orthe clock rate, thereby decreasing power consumption by the CPU. Ingeneral, any technique that can reduce power consumption by the CPU maybe implemented to reduce the overall power consumption.

In one embodiment, the mode selection program 423 may be configured toselect a particular clock for operating the node 400 based on the mode.For example, in the active mode, the mode selection program may selectthe high precision clock 417 to operate the node 400. This may be donebecause, in the active mode, seismic data collection may be in progress,and therefore it may be desirable to use a clock with greater precision.However, because the high precision clock 41 may operate at greaterfrequencies, it may consume more power than the low precision clock.Accordingly, when in the idle mode, the mode selection program 423 maycause the low precision clock to be selected for operating the node 400.

In one embodiment, the mode selection program 423 may be configured toshut off power to one or more devices of the node 400 based on the modeof operation. For example, the idle mode is entered when seismic datacollection is not expected. Accordingly, one or more devices usednecessary for seismic data collection may be powered off. For example,in one embodiment, the power to the particle motion sensors may be shutoff in the idle mode, thereby significantly saving power usage by thenode 400. In one embodiment, the power to the storage device 416 mayalso be shut off in the idle mode because seismic data collection andstorage is not expected.

By selectively shutting off power to certain devices of the node 400and/or operating certain devices in a low power mode while in an idlemode, embodiments of the invention greatly reduce power consumption bythe node, thereby significantly extending the node's life on the seafloor during seismic data collection.

FIG. 6 is a flow diagram of exemplary operations that may be performedby the mode selection program 423, according to an embodiment of theinvention. The operations may begin in step 610 by operating the node400 in an idle mode. As discussed above, operating the node 400 in anidle mode may involve shutting off power to one or more devices of thenode and/or operating one or mode devices in a power savings mode. Instep 620, the mode selection program may determine whether seismic datacollection is expected to occur.

If, in step 620, it is determined that seismic data collection isexpected to occur, then the mode selection program may operate the nodein an active mode, in step 630. As discussed above, operating the nodein an active mode may involve powering most, if not all devices withinthe node. Furthermore, in the active mode, reducing power consumptionmay not necessarily be a priority. Accordingly, node devices that werepreviously in a low power consumption node may be allowed to operate inhigher power consumption modes. For example, the CPU 411 may be operatedat the highest power setting, the high precision clock 417 may be usedin place of the low precision clock 418, and the like.

If, on the other hand, it is determined that seismic data collection isnot expected in step 620, then the mode selection program may maintainthe node in the idle mode (step 610), as illustrated in FIG. 6.

In step 630, the mode selection program may determine whether seismicdata collection has stopped. If it is determined that seismic datacollection has stopped, the operations may proceed to step 610, wherethe node is operated in the power savings mode by the mode selectionprogram 423. On the other hand, if it is determined that seismic datacollection has not stopped, then the mode selection program may continueto operate the node in the active mode, as illustrated in FIG. 6.

Determining whether seismic data collection is expected (step 620 ofFIG. 6) may involve communications between one or more of the sensornodes, a seismic source boat, and/or a hub device (e.g., the surfacebuoy 231 and sea-bed hub 331). For example, in one embodiment, thesensor nodes may be configured to receive a first signal directly froman approaching source boat. Upon detecting the first signal, modeselection program 423 of the node may determine that seismic datacollection is expected.

In an alternative embodiment, a hub device (e.g., the hub 500 of FIG. 5)may be configured to receive the first signal from the source boat. Upondetecting the first signal, the hub device may transfer a second signalto one or more sensor nodes associated with the hub device. The secondsignal may be transferred to the one or more associated nodes via, forexample, a cable connecting the hub device to the one or more sensornodes (e.g., the cables 233 and 333). In other embodiments, the secondsignal may be an electromagnetic signal or an acoustic signal that isrecognized by the one or more associated sensor nodes. Upon receivingthe second signal, the mode selection program 423 of the sensor node maydetermine that seismic data collection is expected.

In one embodiment of the invention, the first signal transferred fromthe source boat to the sensor nodes or the hub device may be an acousticsignal. The acoustic signal may be generated by one or more sourcedevices that are towed by the source boat, according to one embodiment.The sensor nodes and/or the hub device may be configured to receive theacoustic signal and determine that the signal was generated by a sourceboat. In other words, the sensor nodes and/or hub device may distinguishsignals received from a source boat from other noise such as ambientnoise, noise from marine animals splashing in the water, noise fromnearby drilling operations and the like.

In one embodiment, the acoustic sensors in the sensor node and the hubdevice may be actively receiving signals even when in the idle mode,thereby allowing them to receive acoustic signals from the source boat.While operating acoustic sensors in the idle mode is described as anexample herein, in alternative embodiments any type of sensor may beoperated to receive signals from the source boat. In general, less thanall the available sensors are operated so that power savings areachieved while simultaneously maintaining the ability to receivecommunication from a source boat.

FIGS. 7A and 7B illustrate exemplary output of an acoustic sensor, whichmay be used to identify signals from a source boat. FIG. 7A illustratesthe sensor output as amplitude (A) as a function of time (t). In oneembodiment, a signal may be identified as a signal from source boat onlyif the signal is above a predefined threshold amplitude a1 shown in FIG.7A. For example, the signals Sa and Sb in FIG. 7A are below thethreshold a1, and therefore may be disregarded as noise. Signal S1, onthe other hand is above the predefined threshold a1, and therefore maybe recognized as a signal from a source boat.

In some embodiments, to further remove the possibility of noiseencroachment, the sensor nodes and/or the hub devices may be configuredto determine whether a predefined signal sequence has been received. Forexample, referring to FIG. 7A, a signal S2 is received after a timeperiod of about t1 after the signal S1, and a signal S3 is receivedafter a time period of about t2 after the signal S2. The sensor nodesand/or hub devices may be configured to identify predefined sequence ofsignals with predefined separation, duration, frequency, and the like todetermine whether the signal is received from a source boat, therebypreventing the nodes from being activated in response to noise.

FIG. 7B illustrates the output of an acoustic sensor as amplitude (A) asa function of frequency (f). In one embodiment, the sensor nodes and/orhub devices may be configured to determine whether a signal is greaterthan a predefined amplitude threshold a2 and that it falls within apredefined frequency range f_(R). If the thresholds for amplitude andfrequency are met, the signal may be identified as a signal from asource boat.

The signal detection techniques described herein are provided forillustrative purposes only. More generally any technique for correlatinga signal to a source using, for example, a combination of amplitudethresholds, frequency ranges, predefined sequences, and the like may beused to distinguish source boat signals from noise. Furthermore, whileacoustic signals are described as the means for communication betweenthe source boat and nodes/hub devices, in alternative embodiments, anyother type of signal including electromagnetic signals may be used forcommunication using similar techniques for distinguishing noise.

Referring back to step 640 in FIG. 6, determining that seismic dataacquisition has stopped may involve determining that a source boat is nolonger active near the sensor node (or hub device). One way to determinethis may be by determining whether a predefined period of time haspassed since receiving an acoustic signal having predefinedcharacteristics, e.g., frequency range, amplitude, regularity, and thelike.

FIG. 8 is a plan view of an exemplary seismic survey according to anembodiment of the invention. As illustrated a seismic source boat 800 isshown traveling in a direction D over an array of sensor nodes 810. Atthe current position P1 of the source boat 800, a plurality of nodeswithin the zone Z1 represented by the solid circle may be in the activemode for collecting seismic data. In other words, all nodes within apredefined radius of the source boat may be in the active mode. All thenodes completely outside the zone Z1 may be in the idle mode. In oneembodiment, the radius of zone Z1 may represent the distance to whichthe first signal from the source boat to the sensor nodes and/or hubdevice can be reasonably communicated.

FIG. 8 also illustrates a previous position P2 of the boat 800 and theprevious active zone Z2. As can be seen in FIG. 8, the active zone, orthe zone in which the sensor nodes are in the active mode, can bethought of as sliding along with the source boat. While a circularactive zone is shown in FIG. 8, in alternative embodiments, the activezone may have any other shape, whether regular or not. In general,whether a given sensor node is in the active node or not may be afunction of the proximity of the sensor node and/or hub device to thesource boat.

FIG. 9 is a flow diagram of exemplary operations performed whileconducting a seismic survey according to an embodiment of the invention.The operations may begin in step 910 by deploying a plurality of sensornodes on the sea floor, wherein the sensor nodes are initiated in anidle mode. In step 920, seismic data acquisition may be initiated byoperating a seismic source boat. In step 930, as the source boattravels, a plurality of sensor nodes within a predefined distance of thesource boat may be selectively adjusted to operate in the active mode tofacilitate seismic data collection. In step 940, as the source boattravels, sensor nodes that are no longer within a predefined distancefrom the source boat may be adjusted to operate in the idle mode.

While the foregoing is directed to embodiments of the present invention,other and further embodiments of the invention may be devised withoutdeparting from the basic scope thereof, and the scope thereof isdetermined by the claims that follow.

1-25. (canceled)
 26. A method for marine seismic data collection,comprising: operating an array of sensor nodes in an idle mode, whereinthe idle mode is configured to conserve power consumption by the sensornodes; determining whether seismic data is expected at one or more ofthe sensor nodes in the array based on proximity to a vessel configuredto generate a signal for communication with the sensor nodes, whereinthe proximity is determined within a predefined distance of the vesselbased on the signal received from the vessel; in response to determiningthat seismic data is expected, selectively operating the one or moresensor nodes in an active mode; and collecting the seismic data with theone or more sensor nodes while selectively operating in the active mode,wherein sensor nodes within the predefined distance of the vessel areoperating in the active mode and other sensor nodes in the array areoperating in the idle mode.
 27. The method of claim 26, wherein thesignal comprises an acoustic signal used for communication with thesensor nodes.
 28. The method of claim 26, further comprising the vesseltowing a source configured to generate the signal.
 29. The method ofclaim 26, wherein the one or more nodes are configured to identify apredefined sequence of signals with predefined separation, duration andfrequency to prevent the one or more nodes from being activated inresponse to noise.
 30. The method of claim 26, further comprisingdeploying the array of sensor nodes on a sea floor or bed below a watersurface.
 31. The method of claim 30, wherein deploying the array ofsensor nodes comprises deploying the one or more sensors nodes on thesea floor using a remotely operated vehicle.
 32. The method of claim 30,further comprising transferring the signal to the sensor nodes from adevice configured to float at a predefined distance below the watersurface.
 33. The method of claim 30, wherein deploying the array ofsensor nodes comprises programming the one or more sensor nodes tonavigate through a water column to predetermined locations on the seafloor.
 34. The method of claim 30, wherein deploying the array of sensornodes comprises placing the one or more sensor nodes along one or moreocean bottom cables and deploying the one or more ocean bottom cables onthe sea floor.
 35. A marine seismic array comprising: a plurality ofsensor nodes deployed on a sea floor or bed, wherein the sensor nodesare configured to initiate in an idle mode; and a sensor disposed ineach of the sensor nodes, the sensor configured to detect a signalgenerated by a vessel for communication with the sensor nodes; thesensor nodes configured to selectively adjust the idle mode to an activemode based on proximity to the vessel, wherein proximity is determinedwithin a predefined distance of the vessel based on the signal such thatone or more of the sensor nodes operate in the active mode in an activezone of the array, within the predefined distance of the vessel, and thesensor nodes no longer within the predefined distance of the vesselfurther configured to selectively adjust the active mode to the idlemode, such that others of the sensor nodes operate in the idle modeoutside the active zone.
 36. The marine seismic array of claim 35,wherein the sensor disposed in each of the sensor nodes comprises anacoustic sensor configured for detecting the signal.
 37. The marineseismic array of claim 35, wherein the signal comprises anelectromagnetic signal.
 38. The marine seismic array of claim 35,further comprising a source towed by the vessel, wherein the source isconfigured to generate the signal.
 39. The marine seismic array of claim35, further comprising a device configured to transfer the signal to thesensor nodes, the device further configured to float at a predefineddistance below a water surface above the sea floor or bed.
 40. Themarine seismic array of claim 35, wherein the active mode is configuredfor the one or more sensor nodes in the active zone to collect seismicdata while conducting a seismic survey.
 41. The marine seismic array ofclaim 40, wherein the idle mode is configured for the other sensor nodesoutside the active zone to conserve power.
 42. The marine seismic arrayof claim 41, wherein the sensor nodes are configured to operate in theidle mode if it is determined that seismic data collection has stopped,wherein a predefined period of time has passed since receiving thesignal.
 43. A seismic sensor node configured for deployment on a seafloor or bed in an ocean bottom array, the sensor node comprising: aprocessor; at least one acoustic sensor configured to detect an acousticsignal; at least one seismic sensor configured to record seismicsignals; and memory comprising a mode selection program executable onthe processor to perform operations comprising: initiating the sensornode in an idle mode configured to conserve power; determining whetherseismic data is expected at the sensor node based on proximity to avessel configured to generate the acoustic signal for communication withthe sensor node, wherein proximity is determined within a predefineddistance of the vessel based on the acoustic signal; in response todetermining that seismic data is expected at the sensor node: operatingthe sensor node in an active mode; and collecting seismic data while inthe active mode; wherein the sensor node is configured to selectivelyoperate in the active mode to collect the seismic data in an active zoneof the array and to selectively adjust the active mode to the idle modeto conserve power outside the active zone, when no longer within thepredefined distance of the vessel.
 44. The seismic sensor node of claim43, wherein the seismic sensor node is configured for deployment on thesea floor or bed using a remotely operated vehicle.
 45. An ocean-bottomcable comprising a plurality of seismic sensor nodes deployed on the seafloor as recited in claim 43.